Marked maleimide compounds, method for preparing same and use thereof for marking macromolecules

ABSTRACT

Fluorine-18-labelled maleimide compounds of general formula (I): 
                         
in which:
         m represents an integer from 0 to 10;   n represents an integer from 1 to 10;   Y represents a group selected from optionally substituted monocyclic or bicyclic heterocyclic groups;   X represents a radical of formula:
 
(U) a —((CR 1 R 2 ) b —(V) c ) d —((CR 3 R 4 ) e —(W) f ) g —
    in which:   a, b, c, d, e, f and g represent each independently an integer from 0 to 10;   U, V and W represent each independently —NR 1 —, —O—, —S—,       
     
       
         
         
             
             
         
       
         
         
           
              ethynyl, —CR 1 ═CR 2 —, —(C═O)—, —(C═S)—, —C(═NR 1 )—, —C(═O)O—, —(C═S)S—, —C(═NR 1 )NR 2 —, —CR 1 R 2 —, —CR 1 OR 2 — or —CR 1 NR 2 R 3 —. 
           
         
       
    
     Process for preparing these compounds; their use for labelling macromolecules, and complexes of these compounds with a macromolecule. 
     Detection and analysis kit, or diagnosis kit, comprising the said complexes. 
     Use of the complexes in a medical imaging process such as positron emission tomography (PET).

This application is a 371 of PCT/FR03/02028 filed Jun. 30, 2003.

The present invention pertains to maleimide compounds labelled withfluorine-18.

The invention also concerns a process for preparing these compounds.

The invention relates, finally, to the use of these maleimide compounds,especially fluorine-18-labelled maleimide compounds, for labellingmacro-molecules, such as oligonucleotides, proteins, antibodies andpeptides.

The technical field of the invention may be defined in a general manneras being that of the radio-labelling of macromolecules and, inparticular, of proteins and peptides.

The reason for this is that, for use in research or diagnosis,macromolecules, such as proteins or else peptides, can be coupled with alabelling molecule which allows them to be detected; this labellingmolecule may be, for example, a fluorescent molecule, gold particles, aparamagnetic compound or a molecule bearing a radioelement.

Proteins have been radioactively labelled with radioisotopes, iodine andvarious radioisotopes of metals, such as technetium, indium and gallium.More recently proteins have been labelled with fluorine-18.

For example, peptides coupled to radioelements, such as fluorine, allowin vivo detection of the location of thrombotic zones in the event ofvascular accidents of any kind, especially inflammatory and apoptoticfoci, using imaging systems.

Thus radioactive atoms which are short-lived positron emitters, andespecially ¹⁸F, may in particular be detected by positron emissiontomography (PET) instruments.

Owing in particular to the very short half-life of fluorine-18 (in theregion of 109.8 minutes), radio-labelling with fluorine-18 posesspecific problems, which make fluorine-18 labelling fundamentallydifferent from labelling with the other halogens, such as iodine.

The aforementioned coupling may be carried out by any of theconventional techniques of organic chemistry that are known to theskilled person, and by the synthesis of peptide and protein labels whichbear one or more short-lived radioactive atoms, especially ¹⁸F. Thislabel is generally composed, on the one hand, of a moiety capable ofreceiving, for example, an ¹⁸F atom and, on the other hand, of a moietycomprising any conventional function for binding to the macromolecule:for example, to the protein.

These labels must meet the demand for rapid and easy synthesis, since,owing to the short lifetime of radioisotopes such as ¹⁸F, the synthesistime must not generally exceed a few hours.

Moreover, owing to the high radioactivity of the compounds employed,this synthesis must be able to be carried out by robotic means.

Thus processes for labelling proteins or peptides with fluorine-18employ labels which are also called labelled synthons or conjugates, andwhich are placed in three major classes according to whether they reactwith the amine groups, the sulphhydryl groups or the carbohydrate groupsof the macromolecules, such as the proteins and peptides.

Among the compounds or conjugates which react with amino groups mentionmay be made of imidates, such as 3-[¹⁸F]fluoro-5-nitrobenzoimidate,which react, for example, with the ε-NH₂ group of lysine in order tobind to a protein; activated esters, such as N-succinimidyl[¹⁸F]fluorobenzoate; carboxylic acids, such asN-(4-[¹⁸F]fluorobenzoic)acid; aldehydes, such as4-[¹⁸F]-pentafluorobenzaldehyde; and isothiocyanates, such as4-([¹⁸F]fluoromethyl)phenyl isothiocyanate.

Activated halides, such as 4-[¹⁸F]fluorophenacyl bromide, react withamino groups, such as the ε-NH₂ group of lysine or the —SH group ofcysteine.

Amines, such as 1-(4-([¹⁸F]fluoromethyl)-benzoyl)aminobutane-4-amine,react with the CO₂H groups, for example of glutamic acid or of asparticacid, or with the CHO groups of glycoproteins.

Nitrenes with active photochemical centres, such as azidophenacyl[¹⁸F]fluoride, also react with amino groups, for example the ε-NH₂ groupof lysine.

The most effective and most widely described process for labellingproteins and peptides is that employing activated acids, but it is alsothe process which exhibits the greatest non-specificity, since all ofthe nucleophilic sites of the amino acids of the proteins or peptideswill react with the label, conjugate, or labelled synthon.

Two more specific processes for labelling peptides and nucleotidesexhibit high specificity in respect of sulphur atoms, such as those ofcysteine, for example, for the peptides, and of a phosphorothioatefunction, for the nucleotides.

These are, firstly, processes employing halo-acetamide synthons, which,although satisfactory, exhibit the drawback of being very slow and hencepoorly suited to ¹⁸F, owing to the half-life of the latter.

These are; further, processes employing activated maleimides, which areable to attach to the SH groups with a very high specificity, since thereaction is very slow with respect, for example, to the ε-NH₂ sites oflysine.

The scheme of the reaction involving the maleimido group is as follows,in the case of a protein:

in which X represents —S—.

For any labelling, of whatever type, the molecules comprising amaleimide radical are presently considered as being the best, in termsof their reactivity with macromolecules, such as peptides or proteins.

The document of Shiue C.-Y. et al., J. Label. Compounds Radiopharm. 26:287-289 (1989), describes the following compounds:

The first of these compounds is not easy to label with fluorine-18 withhigh specific activity.

This is because only fluorine F₂ would allow ready labelling (as withiodine), and in fact it turns out to be the case that F₂ is generally aproduct with low specific activity.

In particular, F₂ is not suitable for the manufacture of radiotracercompounds, which are, preferentially, a subject of the invention, forthe simple reason that the injected mass of labelled molecule becomessubstantial and that, in that case, the basic principle governing thistracer, namely the extremely low occupancy (for example, less than 5%)of the receptor sites, is not respected.

Moreover, the synthesis of the first of these compounds is difficult: itis, in effect, carried out in four steps, involving a substantialduration, with very low yields, and relatively complex chemicalconversions. This process is therefore not amenable to easy automation.

The second of the compounds cited in the Shiue et al. document containsan amide chain, which is chemically not very robust and which is readilycleaved, or broken, in vivo.

Accordingly its use for diagnostic applications cannot be considered.Moreover, the synthesis of this second compound comprises three stepsand the final yield is low: in the region, for example, of 10% (EOB: endof bombardment, i.e. end of irradiation).

Document U.S. Pat. No. 4,735,792 relates to molecules of formula:

in which X is a radioactive halogen selected from bromine-75,bromine-76, bromine-82, iodine-123, iodine-125, iodine-131 andfluorine-18.

However, the only molecule actually prepared is that labelled withiodine-125.

The preparation of a fluorine-18-labelled molecule is neither mentionednor evidenced, and the comments already made above, with regard to thefirst compound in the Shiue et al. document, also apply in the contextof the document U.S. Pat. No. 4,735,792.

The skilled person, on reading this document, is not in possession ofany information that would allow him or her specifically to prepare afluorine-18-labelled compound, and, if he or she intends doing so, he orshe would employ F₂ and hence would end up with a compound of lowspecific activity, unsuitable for use in PET imaging.

It may be borne in mind, moreover, that the chemistry employed formanufacturing the fluoro compound of the document U.S. Pat. No.4,735,792 is complex and long.

There is therefore a need for fluorine-18-labelled maleimide compoundswhich exhibit high reactivity, high selectivity and a good specificactivity.

There is also a need for fluorine-18-labelled maleimide compounds whichcan be manufactured in a high yield by a process which is simple,reliable, readily automatable, robotizable, rapid and of short duration.

The object of the present invention is to provide a fluorine-18-labelledmaleimide compound which meets these needs, among others.

A further object of the present invention is to provide afluorine-18-labelled maleimide compound which does not exhibit thedrawbacks, deficiencies, limitations and disadvantages of the prior artcompounds and which solves the problems of the prior art.

This object and other, further objects are achieved, in accordance withthe invention, by providing a compound of general formula (I):

in which:

-   -   m represents an integer from 0 to 10, such as 0, 1, 2, 3, 4, 5,        6, 7, 8, 9 or 10;    -   n represents an integer from 1 to 10, such as 1, 2, 3, 4, 5, 6,        7, 8, 9 or 10;    -   Y represents a group selected from mono-cyclic or bicyclic        heterocyclic groups selected from imidazolyl, pyrazolyl,        benzimidazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl,        triazinyl, quinolinyl, isoquinolinyl, cinnolinyl, quinazolinyl,        quinoxalinyl and purinyl groups, it being possible for Y,        optionally, to be substituted by one or more substituents, each        of these substituents being selected independently from        hydrogen, halogens (not radioactive), phenyl, C₁-C₆ alkyl, C₁-C₆        alkoxy, aryloxy, amino, mono- or di(C₁-C₆ alkyl)amino, mono- or        di(aryl) amino, thio, C₁-C₆ alkylthio, arylthio, formyl, C₁-C₆        alkyl-carbonyl, arylcarbonyl, carbonyl, C₁-C₆ alkoxy-carbonyl,        aryloxycarbonyl, C₁-C₆ alkylamino-carbonyl, arylaminocarbonyl        and trifluoromethyl groups;    -   X represents a radical of formula:        (U)_(a)—((CR₁R₂)_(b)—(V)_(c))_(d)—((CR₃R₄)_(e)—(W)_(f))_(g)—        in which:    -   a, b, c, d, e, f and g represent each independently an integer        from 0 to 10, such as 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9;    -   U, V and W represent each independently —NR₁—, —O—, —S—,

-   -    ethynyl, —CR₁═CR₂—, —(C═O)—, —(C═S)—, —C(═NR₁)—, —C(═O)O—,        —(C═S)S—, —C(═NR₁)NR₂—, —CR₁R₂—, —CR₁OR₂— or —CR₁NR₂R₃—, where        R₁, R₂, R₃ and R₄ are each independently selected from hydrogen,        halogens, phenyl, C₁-C₆ alkyl, C₁-C₆ alkoxy, aryloxy, amino,        mono- or di(C₁-C₆ alkyl)amino, mono- or di(aryl)amino, thio,        C₁-C₆ alkylthio, arylthio, formyl, C₁-C₆ alkyl-carbonyl,        arylcarbonyl, carbonyl, C₁-C₆ alkoxy-carbonyl, aryloxycarbonyl,        C₁-C₆ alkylamino-carbonyl, arylaminocarbonyl and trifluoromethyl        groups.

Generally in the present description halogen signifies fluorine,chlorine, bromine or iodine. C₁-C₆ alkyl corresponds to thebranched-chain and linear-chain saturated hydrocarbon radicals having 1to 6 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl andhexyl.

The heterocycles, aryl group, etc., may be attached and substituted inany position.

Similarly ¹⁸F may be attached to Y or X in any position, in particularin any position on a hetero-cycle.

Advantageously, in the compound of formula (I) above, n=1 and Y is a3-pyridinyl group.

The compounds of formula (I) may belong to various classes; a firstclass may be defined as that of “alkyl ethers”, which correspond to theformula (II) below:

in which p is an integer from 1 to 10, such as 2, 3, 4, 5, 6, 7, 8 or 9,and

Preferred compounds of formula (II) are selected from the followingcompounds:

A second class of compounds of formula (I) may be defined as those of“phenylalkyl ethers”, which correspond to the formula (III) below:

in which q and r represent independently an integer from 0 to 10, suchas 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9.

Preferred compounds of formula (III) are selected from the followingcompounds:

A third class is that of compounds which correspond to the formula (IV)below:

in which s is an integer from 1 to 10, such as 2, 3, 4, 5, 6, 7, 8 or 9.

One preferred compound of formula (IV) is the following compound:

A fourth class is that of compounds which correspond to the formula (V)below:

in which t is an integer from 0 to 10, such as 1, 2, 3, 4, 5, 6, 7, 8 or9, and T is a —CH═CH— or —C≡C— group.

Preferred compounds of formula (V) are the following compounds:

The compounds according to the invention have never been described nordisclosed in the prior art.

The compounds according to the invention differ fundamentally from thecompounds of the prior art, owing to their specific structure, in whichthe moiety bearing the fluorine-18 atom is composed, according to theinvention, of a specific group Y which is, in particular, a pyridinylgroup; the binding moiety, for coupling to a macromolecule, such as aprotein or a peptide, is composed, according to the invention, of aspecific function, namely a maleimido function; and, finally, the moietyfor binding to a macromolecule and the moiety bearing the fluorine-18atom are connected, according to the invention, by a spacer arm or chainwhich is again specific, for example of alkyl type (generally 2 to 6C),alkyl ether type, phenylalkyl ether type or alkenyl type, which are notfragile and are not liable to in vivo rupture.

The invention provides for the use of a compound as described above forlabelling macro-molecules.

This macromolecule may be any known macro-molecule, in particular abiological macromolecule, but it may be selected, for example, fromoligonucleotides, proteins, antibodies and peptides. The saidmacro-molecule is advantageously a macromolecule for recognition of aspecific site selected, preferably, from sites exhibiting targetmolecules which are specific of a disease, such as apoptosis sites,necrosis sites or tumour-area sites.

The invention likewise provides a complex comprising a macromoleculecoupled to a compound according to the invention, as described above.

The said macromolecule is selected preferably from oligonucleotides,proteins, antibodies and peptides.

The said coupling is carried out by reacting the double bond of themaleimido group of the compound according to the invention with,specifically, an —SH (thiol) function of cysteine, in the case of apeptide, or a phosphorothioate function, in the case of anoligonucleotide.

This is one of the advantages associated with the specific structure ofthe compounds according to the invention, namely that of allowingspecific, or even exclusive, labelling of cysteines, whereas themajority of other synthons allow only non-specific labelling of lysinesand of cysteines.

The selective or even exclusive labelling of cysteines is due to thepresence in the molecule of the invention of a “dedicated” function,namely the maleimido function, which is a dedicated function forchemoselectivity with regard to the thiols of cysteines, or, similarly,with regard to the phosphoro-thioate functions.

The labelling or coupling, via the cysteine, may be a direct labellingor coupling, in other words such that the cysteine already exists in themacro-molecule which it is desired to couple to the compound accordingto the invention; either cysteine or a molecule (peptide) comprising itmay be introduced (coupled beforehand or not to the compounds of theinvention) into the macromolecule which did not contain cysteine, andthen the coupling is carried out, if it has not been carried outbeforehand on the cysteine or the molecule comprising it.

The cysteine or molecule comprising it may, for example, be introduced“in a tailored fashion” into the macromolecule by protein/peptideengineering in a position in which it does not compete or interfere withthe biological function.

The said macromolecule is advantageously a macromolecule for recognitionof a specific site, as described above. The coupling, i.e. labelling, ispreferably such that it does not affect the recognition activity of thetarget, the site, by the macromolecule.

The invention likewise provides a detection and analysis kit, formedical imaging, for example, comprising a compound according to theinvention and a macromolecule.

The invention likewise provides a detection and analysis kit, formedical imaging, for example, comprising a compound according to theinvention coupled to a macromolecule, in other words a complex accordingto the invention.

The invention also provides a diagnosis kit comprising a compoundaccording to the invention and a macromolecule.

The invention further provides a diagnosis kit comprising a complex asdescribed above.

The invention provides, finally, for the use of the complex or compoundas described above in a medical imaging process, such as positronemission tomography (PET), and for the use of a complex or compoundaccording to the invention for manufacturing a product intended formedical imaging, for example for positron emission tomography (PET).

Lastly the invention provides a product for medical imaging, especiallypositron emission tomography (PET), comprising a complex or a compoundas described above and a pharmaceutically acceptable vehicle.

In their application, in the context of PET, the compounds and complexesaccording to the invention, comprising a fluorine-18 atom, exhibitnumerous advantages over compounds with another radioactive halogen, forexample iodine.

This is because the only positron-emitting isotope of iodine isiodine-124, which could allow PET.

However, it is still produced in small amounts (a few mCi as againstcuries for F-18). It is also difficult to produce. Finally, iodine-124is not a pure positron emitter (in contrast to fluorine-18, 97%) anddecays by beta+emission to only 25% and by electron capture to 75%; itpossesses a large number of gamma rays, ranging from 0.603 MeV (62%) to2.75 MeV (1%).

The invention likewise provides a process for preparing a compound offormula (I), as described above, in which:

a) a precursor compound of formula (Ia):

in which PR₁ and PR₂ represent independently a hydrogen atom or aprotective group for the amine function, with the proviso that PR₁ andPR₂ are not both (simultaneously) a hydrogen atom, or else PR₁ and PR₂,together with the nitrogen atom, form a cyclic protective group for theamine function, Gp represents a leaving group capable of being replacedby a fluorine-18 atom, and X, Y, m and n are as already defined above,is contacted with a source of [¹⁸F]-labelled fluoride ions F⁻ to give acompound of formula (Ib):

b) the protective group(s) PR₁ and/or PR₂ is or are removed from theamine function in the compound (Ib), to give a compound of formula (Ic):H₂N—(X)_(m)—(Y)_(n)—¹⁸F  (Ic)

c) the compound (Ic) is reacted with a reactant capable of giving amaleimido group from an amino group, to give the final compound offormula (I).

The process according to the invention is simple, reliable and easy toimplement and can be easily robotized. It comprises only three steps,including one which is an extremely simple deprotection step.

The overall duration of the process is low: by way of example, it isgenerally from 60 to 120 minutes, preferably from 75 to 85 minutes.

The incorporation of the halogen, fluorine-18, is accomplished extremelyeffectively with a high yield, for example 70% to 100%, because, inparticular, it is performed on a heterocyclic group, such as pyridine.

The final yield of the entirety of the process for a purified product isextremely high, for example from 15% to 25%, and the potentialquantities of synthon compound, at the end of synthesis, are also verylarge.

In the compound (Ia) the groups PR₁ and PR₂, when they are protectivegroups, may be any protective group known in organic chemistry. They arepreferably selected from the groups tert-butoxycarbonyl (BOC) andfluorenylmethoxycarbonyl (FMOC).

When PR₁ and PR₂, together with the nitrogen atom of the amine function,form a protective group for that function, this protective group may be,for example, a phthalimido group.

In the compound (Ia) the group Gp may be any leaving group capable ofbeing replaced by an atom of fluorine-18; Gp is preferably selected fromhalogens, such as F, Cl, Br and I, mesyl, tosyl and triflate groups,when Y is an alkyl group; and Gp is preferably selected from halogens,ammonium salts, such as trimethylammonium trifluoromethanesulphonate,and the nitro group, when Y is an aromatic or heterocyclic group.

In step a) the source of ¹⁸F-labelled fluoride ions comprises the saidfluoride ions and a counterion selected from large-sized cations, suchas rubidium and tetrabutylammonium, and small-sized cations, such aspotassium, sodium and lithium, the said small-sized cations beingtrapped, stabilized, for example, by a cryptand or a crown ether, etc.,the said cryptand or crown ether being adapted to the small-sized cationemployed.

One example of the cryptand is the product Kryptofix® K₂₂₂:(4,7,13,16,21,24-hexaoxa-1,10-diazabi-cyclo[8.8.8]hexacosane), whichtraps, for example, the potassium ion.

The counterion or cation may be brought into the form of any salt: forexample, it may be K₂CO₃ in the case of potassium.

Step a) is generally carried out in a solvent, which may be anyappropriate solvent, such as DMSO.

Step a) may be carried out under conditions known to the skilled person,with heating generally at a temperature from 50 to 200° C., for example,145° C., for a time of generally from 1 to 30 minutes, for example from4 to 6 minutes.

Step b), the step of removing the protective group from the aminefunction, i.e. the deprotection step, to give the compound of formula(Ic) in which the amino group is free, may be carried out by any knownprocess of deprotection. It will be possible, for example, to contactthe compound (Ib) with TFA in CH₂Cl₂ for a time of generally from 1 to 5minutes, for example 2 minutes. It should be noted that TFA is generallyused only if the protective group is removed in an acid medium, forexample when PR₁═BOC and PR₂═H.

In step c) the reactant capable of giving a maleimido group from anamido group may be any known compound. It will therefore be possible forit to be selected from N-methoxycarbonylmaleimide and succinimide.

Step c) may be carried out under conditions known to the skilled person,for example in a solvent such as xylene or THF, with heating generallyat a temperature of from 100 to 200° C., for example 190° C., for a timeof from 1 to 20 minutes, for example 5 minutes.

Step c) may in another embodiment also be carried out in a two-phasemixture, for example of dioxane and aqueous sodium bicarbonate, atambient temperature for a time of from 3 to 15 minutes, for example 10minutes; this embodiment of step c) offers the advantage of giving abetter yield and of being implemented at ambient temperature, with noneed to heat the mixture.

The compound of formula (Ia) may correspond to the formula (IIa) below:

The compound (IIa) preferably corresponds to the formula (IIb) below:

The compound of formula (Ia) may, in another embodiment, correspond tothe formula (IIIa) below:

The compound (IIIa) preferably corresponds to the formula (IIIb) below:

The compound of formula (Ia) may, in yet another embodiment, correspondto the formula (IVa) below:

The compound (IVa) preferably corresponds to the formula (IVb) below:

In another embodiment the compound of formula (Ia) may correspond to theformula (Va) below:

The compound (Va) preferably corresponds to the formula (Vb) below:

The invention likewise provides the precursor compounds of formulae(Ia), (IIa), (IIb), (IIIa), (IIIb), (IVa), (IVb), (Va) and (Vb), asdescribed above, as synthesis intermediates for the compounds offormulae (I) to (V) according to the invention.

The precursor compounds may be selected in particular from the finalcompounds defined and set out above, in which the [¹⁸F] is replaced by anon-radio-active halogen, such as ¹⁹F, Cl, Br or I, an ammonium salt,such as trimethylammonium trifluoromethane-sulphonate, or an NO₂ groupand the 1-pyrrole-2,5-dione group is replaced by atert-butoxycarbonylamino group.

Preferred precursor compounds are, for example,[3-(3-tert-butoxycarbonylaminopropoxy)pyridin-2-yl]-trimethylammoniumtrifluoromethanesulphonate and the tert-butyl ester of[3-(2-nitropyridin-3-yloxy)propyl]-carbamic acid.

The invention will now be set out in more detail in the descriptionwhich follows, which is given by way of illustration and not oflimitation, in relation to preparation examples of compounds accordingto the invention and of complexes according to the invention.

Experimental Conditions

Chemical products, thin-layer chromatography (TLC) and high-pressureliquid chromatography (HPLC).

The chemical products were obtained from a variety of suppliers(Aldrich, Fluka or Sigma France) and were used without furtherpurification unless mentioned otherwise. The TLCs are carried out onplates precoated with silica gel 60F₂₅₄ from Merck. The compounds werelocated (1) if possible at 254 nm, using a UV lamp, and/or (2) bystaining with iodine and/or (3) by immersing the TLC plates in anethanolic 1% ninhydrin solution (or an aqueous 1% KMnO₄ solution) and byheating on a hot plate. The radioactive dots, marks or spots aredetected using a Berthold Trace Master 20 automatic linear analysisinstrument.

Spectroscopies

The chemical NMR spectra are recorded on a Bruker AMX instrument (300MHz), using the hydrogen residue of the deuterated solvents (DMSO-d₆, δ:2.50 ppm; CD₂Cl₂, δ: 5.32 ppm; CD₃OD, δ: 4.78; CD₃CN, δ: 1.93 ppm)and/or TMS as internal standards for ¹H NMR, and the deuterated solvents(DMSO-d₆, δ: 39.5 ppm; CD₂Cl₂, δ: 53.8 ppm; CD₃OD, δ: 49.3 ppm) and/orTMS as internal standards for ¹³C NMR.

The chemical shifts are given in ppm with TMS (tetramethylsilane) asreference, the chemical shift of which is set at 0. s, d, t, dd, q, q5,m and b represent singlet, doublet, triplet, doublet of a doublet,quadruplet, quintuplet, multiplet, and broad, respectively. The massspectra (MS) are measured on a Quadripolair Finnigan 4 600 instrument(DCI/NH₄ ⁺).

Production of the Radioactive Isotope

Aqueous [¹⁸F] fluoride ions were prepared in a CGR-MeV 520 cyclotron byirradiation of a 2 ml water target, using a 20 MeV proton beam on 95%[¹⁸O]-enriched water by the nuclear reaction [¹⁸O(p, n)¹⁸F]. Thefluoride ions were transferred into the appropriate shielded cell.Typical production: 550-650 mCi (20.3 to 24.0 GBq) of [¹⁸F]F⁻ at the endof bombardment for irradiation of 20 μA for 30 minutes (36 000 μC).

Miscellaneous

The radiosyntheses using fluorine-18, including the purifications bysemi-preparative HPLC, were carried out in a 7.5 cm cell shielded withlead, using a computer-controlled Zymate robot system (from ZymackCorp., USA). Microwave activation is carried out with a Microwell 10oven (2.45 GHz) supplied by Labwell AB, Sweden.

The specific radioactivity is determined as follows: the surface area ofthe UV absorption peaks, corresponding to the radiolabelled product, ismeasured on the HPLC chromatogram and compared with a calibration curvegiving the mass as a function of the UV absorption.

EXAMPLE 1 General procedure for the Mitsunobu coupling of3-(N-tert-butylcarbonylamino)-1-propanol with various 2-substituted3-hydroxypyridine derivatives.

A solution of 3.0 g of triphenylphosphine (molecular mass: 262.69; 11.4mmol) in THF (60 ml) is admixed with 1.8 ml of diethyl azodicarboxylate(DEAD, molecular mass: 174.16; d: 1.106; 11.4 mmol; 1 eq). Afterstirring at 0° C. for 10 to 15 minutes 1.95 ml of3-(N-tert-butoxycarbonylamino)-1-propanol (molecular mass: 175.23; d:1.025; 11.4 mmol; 1 eq) and the 2-substituted 3-hydroxypyridinederivative (11.4 mmol; 1 eq) are added. The mixture is stirred atambient temperature overnight and then concentrated to dryness. Theresidue is taken up with CH₂Cl₂ and the solution obtained is washed withaqueous 10% NaHCO₃ solution, water and brine and dried with Na₂SO₄before being concentrated to dryness. The residue is chromatographed onsilica gel to give the desired derivative:3-[3-(N-tert-butyloxycarbonylamino)-1-propoxy]pyridine (or tert-butylester of [3-(pyridin-3-yloxy)propyl]carbamic acid).

EXAMPLE 2 General procedure for deprotecting N-tert-butoxycarbonylaminofunctions with TFA.

From 3 to 7 mmol of the appropriate tert-butyl ester of[3-(pyridin-3-yloxy)propyl]carbamic acid in 5 ml of CH₂Cl₂ are admixedwith 2 ml of TFA. The solution is stirred at ambient temperature for 45minutes and concentrated to dryness.

The residue is redissolved in 2 ml of CH₂Cl₂ and again concentrated todryness (twice) to give 3-(pyridin-3-yloxy)propylamine, in the form ofan oily residue.

EXAMPLE 3 General procedure for forming the maleimido derivative.

From 2 to 3 mmol of the appropriate 3-(pyridin-3-yloxy)propylamine in 5ml of THF are admixed in succession with 500 mg of maleic anhydride(molecular mass: 98.06; 5.1 mmol) and 200 mg of p-toluenesulphonic acidhydrate (molecular mass: 190.22; 1.0 mmol). The solution is refluxed for24 hours and concentrated to dryness. The residue is chromatographed onsilica gel to give the desired1-[3-(pyridin-3-yloxy)propyl]-pyrrole-2,5-dione derivative.

EXAMPLE 4 Preparation of 2-fluoro-3-hydroxypyridine

100 ml of pyridine hydrofluoride (Py. (HF)_(x), from Fluka, 70% of thesample consisting of hydrogen fluoride, 30% of the sample consisting ofpyridine), cooled at 0° C., are admixed cautiously and in successionwith 3.7 g of 2-amino-3-hydroxypyridine (molecular mass: 110.12; 33.6mmol) and 3 g of NaNO₂ (molecular mass: 69.00; 43.5 mmol). The mixtureis stirred at 0° C. for 1 hour and then slowly rendered basic with 10Naqueous NaOH solution, transferred to a decanter and extracted withEtOAc. The organic phases are combined, washed with water and brine,dried with Na₂SO₄ and concentrated to dryness. The residue is purifiedby passing it through a silica gel column (eluent: heptane/EtOAc: 50/50)to give 2.5 g (65%) of 2-fluoro-3-hydroxypyridine in the form of asolid, which is used without further purification.

Rf(EtOAc/heptane: 80/20): 0.65. m.p.: 131° C. ¹H NMR (DMSO-d₆, 298 K):δ: 10.41 (s, 1H); 7.64 (td, J: 1.7 & 4.7 Hz, 1H); 7.42 (dd, J: 1.7, 1.7& 10.8 Hz, 1H); 7.17 (ddd, J: 1.3, 4.7 & 7.8 Hz, 1H). ¹³C NMR (DMSO-d₆298 K): δ: 152.8 (d, J¹ _(F-C): 233 Hz, C; 140.2 (d, J² _(F-C): 27 Hz,C); 135.6 (d, J³ _(F-C)) 13 Hz, CH) 126.2 (d, J³ _(F-C): 5 Hz, CH);122.6 (CH).MS(DCI/NH₄ ⁺): C₅H₄FNO: 131[M+NH₄ ⁺]; 114[M+H⁺]. Anal.(C₅H₄FNO) C, H, N.

EXAMPLE 5

In this example the preparation is described of a reference molecule,which is 1-[3-(2-fluoropyridin-3-yloxy)propyl]pyrrole-2,5-dione in whichthe fluorine is not radioactive fluorine but ¹⁹F.

a) Preparation of the tert-butyl ester of[3-(2-fluoropyridin-3-yloxy)propyl]carbamic acid

The procedure described above in Example 1 is used, with the2-fluoro-3-hydroxypyridine prepared in Example 4 (1.29 g; 11.4 mmol), togive 1.9 g (62%) of the tert-butyl ester of[3-(2-fluoropyridin-3-yloxy)-propyl]carbamic acid in the form of ayellow oil, after flash chromatography (eluent:pure CH₂Cl₂,heptane/EtOAc: 70/30 to 50/50).

Rf(CH₂Cl₂/EtOAc: 95/5): 0.45. ¹H NMR (CD₂Cl₂, 298 K): δ: 7.68 (dt, J:4.8 & 1.8 Hz, 1H); 7.28 (td, J: 7.8 & 1.5 Hz, 1H); 7.10 (dd, J: 5.1 &0.9 Hz, 1H); 4.96 (b, w_(1/2): 20 Hz, 1H); 4.07 (t, J: 6.0 Hz, 2H); 3.28(q, J: 6.0 Hz, 2H); 1.98 (q⁵, J: 6.0 Hz, 2H); 1.39 (s, 9H). ¹³C NMR(CD₂Cl₂, 298 K): δ: 156.3 (C); 154.1 (d, J¹ _(F-C): 235 Hz, C); 142.5(d, J² _(F-C): 25 Hz, C); 137.5 (d, J³ _(F-C): 13 Hz, CH); 123.0 (CH);122.2 (CH); 79.2 (C); 67.3 (CH₂); 38.0 (CH₂); 29.8 (CH₂); 28.5 (CH₃).

b) Preparation of 3-(2-fluoropyridin-3-yloxy)-propylamine

The procedure described above in Example 2 is used, with the tert-butylester of [3-(2-fluoropyridin-3-yloxy)propyl]carbamic acid prepared in a)(1.0 g; molecular mass: 270.30; 3.7 mmol), to give 1.4 g (95%) of3-(2-fluoropyridin-3-yloxy)propylamine.2TFA, in the form of a yellowoil.

¹H NMR (CD₃OD, 298 K): δ: 7.51 (bt, J<2.0 Hz, 1H); 7.36 (bt, J<3.0 Hz,1H); 7.04 (bq, J<3.0 Hz, 1H); 4.03 (t, J: 6.0 Hz, 2H); 2.99 g (Q, J: 6.0Hz, 2H); 2.01 (q⁵, J: 6.0 Hz, 2H). ¹³C NMR (CD₃OD, 298 K): δ: 159.3 (q,J² _(F-C): 41 Hz, C, CF₃CO₂H); 155.3 (d, J¹ _(F-C): 237 Hz, C); 143.5(d, J² _(F-C): 24 Hz, C); 138.5 (d, J³ _(F-C): 13 Hz, CH); 125.1 (CH);123.8 (CH); 116.4 (q, J¹ _(F-C): 284 Hz, C, CF₃, CO₂H); 67.9 (CH₂), 38.6(CH₂); 29.4 (CH₂).

c) 1-[3-(2-Fluoropyridin-3-yloxy)propyl]-pyrrole-2,5-dione

The procedure described above in Example 3 is used, with3-(2-fluoropyridin-3-yloxy)propylamine.2TFA (1.0 g; molecular mass:398.23; 2.5 mmol) to give 310 mg (48%) of1-[3-(2-fluoropyridin-3-yloxy)propyl]-pyrrole-2,5-dione, in the form ofa yellow powder, after flash chromatography (eluent: heptane/EtOAc:50/50 to 30/70). For analytical purposes an aliquot fraction (100 mg)was purified again by preparative or semi-preparative HPLC.

Rf(EtOAc): 0.7. Rf(EtOAc/heptane: 80/20): 0.5. ¹H NMR (CD₂Cl₂, 298 K):δ: 7.69 (bd, J: 3.0 Hz, 1H) 7.27 (t, J: 6.0 Hz, 1H); 7.11 (dd, J: 3.0 &6.0 Hz, 1H); 6.69 (s, 2H); 4.05 (t, J: 6.0 Hz, 2H); 3.82 (t, J: 6.0 Hz,2H); 2.11 (q⁵, J: 6.0 Hz, 2H). ¹³C NMR (CD₂Cl₂, 298 K): δ: 171.2 (2×C);154.0 (d, J¹ _(F-C): 235 Hz, C); 142.4 (d, J² _(F-C): 25 Hz, C); 137.7(d, J³ _(F-C): 13 Hz, CH); 134.5 (2×CH); 123.2 (CH); 122.2 (CH); 67.5(CH₂); 35.4 (CH₂); 28.5 (CH₂). MS (DCI/NHR⁺): C₁₂H₁₁FN₂O₃: 251 (M+H⁺].

EXAMPLE 6 Preparation of the tert-butyl ester of[3-(2-nitropyridin-3-yloxy)propyl]carbamic acid

The procedure described above in Example 1 is used, with2-nitro-3-hydroxypyridine (1.6 g; molecular mass: 140.10; 11.4 mmol), togive 2.2 g (65%) of the tert-butyl ester of[3-(2-nitropyridin-3-yloxy)propyl]-carbamic acid in the form of a yellowoil, after flash chromatography (eluent: heptane/EtOAc: from 60/40 to40/60). For analytical purposes an aliquot fraction (100 mg) is purifiedagain on a preparative or semi-preparative HPLC apparatus.

Rf(EtOAc/heptane: 50/50): 0.35. ¹H NMR (CD₂Cl₂, 298 K): δ: 8.04 (t, J:3.0 Hz, 1H); 7.53 (d, J: 3.0 Hz, 2H); 4.95 (b, w_(1/2): 15 Hz, 1H); 4.18(t, J: 6.0 Hz, 2H); 3.26 (q, J: 6.0 Hz, 2H); 1.99 (q⁵, J: 6.0 Hz, 2H);1.40 (s, 9H). ¹³C NMR (CD₂Cl₂, 298 K): δ: 156.3 (C); 149.2 (C); 147.3(C); 139.5 (CH); 129.2 (CH); 124.0 (CH); 79.2 (C); 68.3 (CH₂); 37.9(CH₂); 29.5 (CH₂); 28.4 (CH₃).

EXAMPLE 6a Preparation of[3-(3-tert-butoxycarbonylamino-propoxy)pyridin-2-yl]trimethylammoniumtrifluoro-methanesulphonate

The procedure described above in Example 1 is used, with2-dimethylamino-3-hydroxypyridine (0.250 g; molecular mass: 138.17; 1.8mmol), to give 0.290 g of the tert-butyl ester of[3-(2-dimethylaminopyridin-3-yloxy)propyl]carbamic acid (58%) in theform of a yellow oil after flash chromatography (eluent: heptane/EtOAc:from 70/30 to 50/50).

Rf (CH₂Cl₂/EtOAc: 50/50): 0.30. ¹H NMR (CD₂Cl₂, 298 K): δ: 7.79 (dd, J:4.0 & 1.5 Hz, 1H); 7.00 (dd, J: 7.8 & 1.2 Hz, 1H); 6.73 (dd, J: 7.8 &4.8 Hz, 1H); 5.15 (b, w_(1/2): 15 Hz, 1H); 4.02 (t, J: 6.0 Hz, 2H); 3.30(q, J: 6.0 Hz, 2H); 2.95 (s, 6H); 1.99 (q⁵, J: 6.0 Hz, 2H); 1.42 (s,9H). ¹³C NMR (CD₂Cl₂, 298 K): δ: 156.2 (C); 153.7 (C); 146.2 (C); 139.0(CH); 118.8 (CH); 115.9 (CH); 79.1 (C); 67.4 (CH₂); 41.1 (CH₃); 38.8(CH₂); 32.3 (CH₂); 28.5 (CH₃).

The tert-butyl ester of[3-(2-dimethylamino-pyridin-3-yloxy)propyl]carbamic acid is subsequentlydiluted in toluene (2 ml per 100 mg of ester) and the solution is cooledto 0° C. (ice bath). This solution is admixed with methyltrifluoromethanesulphonate (50 microlitres per 100 mg of ester) and thereaction mixture is stirred at 0° C. for 1 hour. The precipitate of[3-(3-tert-butoxycarbonylaminopropoxy)pyridin-2-yl]-trimethylammoniumtrifluoromethanesulphonate is filtered off, washed with small portionsof ethyl ether and dried under vacuum to give a fine white powder (145mg per 100 mg of ester).

¹H NMR (CD₂Cl₂, 298 K): δ: 8.09 (dd, J: 3.3 & 1.0 Hz, 1H); 7.67 (bd, J:8.0 Hz, 1H); 7.61 (dd, J: 7.0 & 4.2 Hz, 1H); 5.20 (b, w_(1.2): 15 Hz,1H); 4.31 (t, J: 6.3 Hz, 2H); 3.71 (s, 9H); 3.31 (q, J: 6.3 Hz, 2H);2.12 (q⁵, J: 6.3 Hz, 2H); 1.38 (s, 9H). ¹³C NMR (CD₂Cl₂, 298 K): δ:156.6 (C); 147.7 (C); 142.6 (C); 139.0 (CH); 129.0 (CH); 124.6 (CH);121.2 (q, J: 319 Hz, CF₃); 79.3 (C); 68.1 (CH₂); 54.8 (CH₃); 37.5 (CH₂);30.0 (CH₂); 28.4 (CH₃).

EXAMPLE 7

In this example the preparation is described of a compound according tothe invention, which is1-[3-(2-[¹⁸F]fluoropyridin-3-yloxy)propyl]pyrrole-2,5-dione.

a) K[¹⁸F]F—K₂₂₂ Complex

In order to recover and recycle the [¹⁸O]water target, it is passedthrough an anion exchange resin (AGlx8 from Bio-Rad, 100-200 mesh). The[¹⁸F]fluoride ion is then eluted from the resin, using 1.0 ml of anaqueous 4.5 mg/ml K₂CO₃ solution.

Following addition of 11.0 to 15.0 mg of Kryptofix® K₂₂₂(4,7,13,16,21,24-hexaoxa-1,10-diaza-bicyclo[8.8.8]hexacosane), theresulting solution is then gently concentrated to dryness at 145-150° C.under a stream of nitrogen for 10 minutes, to give a pure K[¹⁸F]F—K₂₂₂complex, in the form of a semi-solid white residue.

b) 1-[3-(2-[¹⁸F]Fluoropyridin-3-yloxy)propyl]-pyrrole-2,5-dione

Freshly distilled DMSO (600 μl), containing 4.0 to 6.0 mg of the “nitro”labelled precursor (tert-butyl ester of[3-(2-nitropyridin-3-yloxy)propyl]carbamic acid), is added directly tothe tube containing the dried K[¹⁸F]-K₂₂₂ complex. The tube (unsealed)is then placed in a heating block (at 145° C. for 4 minutes). The tubeis subsequently cooled using an ice/water bath and the remainingradioactivity is measured.

85% to 95% of the initial activity placed in the container is stillpresent. The reaction mixture obtained, which is dark in colour, is thenanalysed by radiochromatography. The incorporation yields are calculatedfrom the TLC radiochromatogram and are defined by the ratio of surfacearea of the tert-butyl ester derivative of[3-(2-[¹⁸F]fluoropyridin-3-yloxy)-propyl]carbamic acid to the totalfluorine-18 (¹⁸F) activity (SiO₂-TLC; eluent: EtOAc; Rf: 0.75 and Rf:[¹⁸F]fluoride ion: 0.0). The reaction mixture is diluted with 1 ml ofwater and transferred to a C18 Sep-pak cartridge (Waters). The tube isrinsed twice with 1 ml of water, which is also transferred and added tothe dilute reaction mixture in the cartridge.

Subsequently the entire system is passed through the cartridge. Thecartridge is washed with 3 ml of water and partly dried for 0.5 minute,during which a stream of nitrogen is passed through.

The tert-butyl ester derivative of[3-(2-[¹⁸F]-fluoropyridin-3-yloxy)propyl]carbamic acid is eluted fromthe cartridge with 3 ml of dichloromethane into a reaction flaskcontaining 0.1 ml of TFA. 2 times 1 ml of dichloromethane are used towash the cartridge and to effect complete transfer of the abovementioned[¹⁸F]-labelled derivative (5% of the total amount of radio-activity,involved in the fluorination process, remains in the cartridge). Theincorporation yield is also confirmed, after the elution of the Sep-pak,by the ratio of the CH₂Cl₂ counting values to total radio-activityeluted (DMSO/H₂O+CH₂Cl₂). The resulting solution, CH₂Cl₂/TFA (50/1,v/v), is concentrated to dryness (at 65-75° C.) under a moderate streamof nitrogen for 4 to 6 minutes. The yield of the deprotection isquantitative: no above described molecule protected with BOC can bedetected by radio-chromatography. The above residue is redissolved in 2ml of CH₂Cl₂ and concentrated to dryness again in order to minimize thepresence of TFA (at 65-75° C. under a moderate stream of nitrogen for 4to 6 minutes). The residue is then diluted with 0.5 ml of xylenecontaining 25 mg of N-methoxycarbonylmaleimide. The container is thenhermetically sealed, heated at 190° C. (strong reflux) for 5 minutes andthen cooled for 2 minutes, using an ice/water bath. The reaction mixtureis then injected into a semi-preparative HPLC column. Isocratic elution[eluent: heptane/EtOAc: 50/50; flow rate: 6.0 ml/minute] gives pure,labelled 1-[3-(2-[¹⁸F]fluoropyridin-3-yloxy)propyl]pyrrole-2,5-dione;retention time: 7.5 to 8.0 minutes.

Typically, 60 to 70 mCi of pure, labelled1-[3-(2-[¹⁸F]fluoropyridin-3-yloxy)propyl]pyrrole-2,5-dione can beobtained in 75 to 85 minutes, from 550-650 mCi of an [¹⁸F]F⁻ productionbatch from a cyclotron.

EXAMPLE 7a

The fluorine-18-labelled compound,1-[3-(2-[¹⁸F]fluoropyridin-3-yloxy)propyl]pyrrole-2,5-dione, may also beprepared by repeating steps a) and b) of the process described inExample 7, still using as labelling precursor the “nitro” compound(tert-butyl ester of [3-(2-nitropyridin-3-yloxy)propyl]carbamic acid),but by modifying the final part of the preparation (step c)) as follows(variant according to which step c) is carried out in a two-phasemixture of dioxane and aqueous sodium bicarbonate).

Following deprotection of the amine function (TFA/CH₂Cl₂) the residueobtained after concentration to dryness is taken up in 0.250 ml ofdioxane containing 25 mg of N-methoxycarbonylmaleimide. This solution isadmixed with 0.750 ml of a saturated aqueous sodium bicarbonate solutionand the preparation is vortexed at ambient temperature for 10 minutes.The reaction mixture is subsequently diluted with 1 ml of water andtransferred to a C18 Sep-pak cartridge (Waters). The flask is rinsedtwice with 1 ml of water, which is likewise transferred and added to thedilute reaction mixture in the cartridge. Finally 8 ml of water are alsoadded to the dilute reaction mixture in the cartridge. The system issubsequently passed into the cartridge. The cartridge is washed with 3ml of water and partly dried for 0.5 minute, during which a stream ofnitrogen is passed through. The fluorine-18-labelled derivative(1-[3-(2-[¹⁸F]fluoropyridin-3-yloxy)propyl]-pyrrole-2,5-dione) is elutedfrom the cartridge with 3 ml of dichloromethane in a new, empty flask.Two times 1 ml of dichloromethane are used to wash the cartridge and toeffect complete transfer of the [¹⁸F]-labelled derivative mentionedabove. The solution containing the [¹⁸F]-labelled derivative mentionedabove is concentrated (at 65-75° C., under a moderate stream ofnitrogen, for 3 to 5 minutes) to a volume of approximately 1 ml andinjected into a semi-preparative HPLC column. Purification is identicalto that described in Example 7.

EXAMPLE 7b

The fluorine-18-labelled compound,1-[3-(2-[¹⁸F]fluoropyridin-3-yloxy)propyl]pyrrole-2,5-dione, may also beprepared by repeating steps a) and b) of the process described inExample 7 or 7a, but using, as labelling precursor, the“trimethylammonium trifluoromethanesulphonate” compound([3-(3-tert-butoxycarbonylaminopropoxy)pyridin-2-yl]trimethylammoniumtrifluoromethanesulphonate).

EXAMPLE 8

In this example the labelling of a peptide is described, namely thepeptide N-acetyl-Lys-Ala-Ala-Ala-Ala-Cys-amide, with a compoundaccording to the invention, which is1-[3-(2-[¹⁸F]fluoropyridin-3-yloxy)-propyl]pyrrole-2,5-dione.

The procedure is as follows:

One equivalent of peptide (2 mg/ml; 200 nmol; 36.2 μl) in solution in 50mM Tris, 150 mM NaCl buffer, pH=7.4 is admixed with 1 equivalent of TCEPin Tris buffer (7.9 mg/ml; 7.3 μl; 200 nmol). The sample is left atambient temperature for 5 minutes and then diluted in 1 ml of Trisbuffer. The dry synthon,1-[3-(2-[¹⁸F]fluoropyridin-3-yloxy)propyl]pyrrole-2,5-dione, is taken upin 100 μl of a 50/50 heptane/ethyl acetate mixture, and the solution ofreduced peptide is added. The sample is left at ambient temperature for10 minutes, stirring from time to time. The labelled peptide is purifiedby HPLC on a C18 column with a gradient from 0 to 34% acetonitrile/0.1%TFA in H₂O/0.1% TFA over 30 minutes (DeltaPak C18 column,R_(t-peptide)=28 min)

1. A compound according to formula (I):

wherein m represents an integer from 0 to 10; n represents an integerfrom 1 to 10; Y represents a monocyclic or bicyclic heterocyclic groupselected from the group consisting of imidazolyl, pyrazolyl,benzimidazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl,triazinyl, quinolinyl, isoquinolinyl, cinnolinyl, quinazolinyl,quinoxalinyl and purinyl, wherein Y may optionally be substituted withone or more substituents selected from the group consisting of hydrogen,halogen, phenyl, C₁-C₆ alkyl, C₁-C₆ alkoxy, aryloxy, amino, mono- ordi(C₁-C₆ alkyl)amino, mono- or di(aryl)amino, thio, C₁-C₆ alkylthio,arylthio, formyl, C₁-C₆ alkyl-carbonyl, arylcarbonyl, carbonyl, C₁-C₆alkoxy-carbonyl, aryloxycarbonyl, C₁-C₆ alkylamino-carbonyl,arylaminocarbonyl and trifluoromethyl; and X represents a radical of thefollowing formula:(U)_(a)—((CR₁R₂)_(b)—(V)_(c))_(d)—((CR₃R₄)_(e)—(W)_(f))_(g)—  wherein a,b, c, d, e, f and g each independently represent an integer from 0 to10; and U, V and W each independently represent —NR₁—, —O—, —S—,—N(—O)—, ethynyl, —CR₁═CR₂—, —(C═O)—, —(C═S)—, —C(═NR₁)—, —C(═O)O—,—(C═S)S—, —C(═NR₁)NR₂—, —CR₁R₂—, —CR₁OR₂— or —CR₁NR₂R₃—, wherein R₁, R₂,R₃ and R₄ are each independently selected from the group consisting ofhydrogen, halogen, phenyl, C₁-C₆ alkyl, C₁-C₆ alkoxy, aryloxy, amino,mono- or di(C₁-C₆ alkyl)amino, mono- or di(aryl)amino, thio, C₁-C₆alkylthio, arylthio, formyl, C₁-C₆ alkyl-carbonyl, arylcarbonyl,carbonyl, C₁-C₆ alkoxy-carbonyl, aryloxycarbonyl, C₁-C₆alkylamino-carbonyl, arylaminocarbonyl and trifluoromethyl.
 2. Thecompound according to claim 1, wherein n is 1 and Y is a 3-pyridinylgroup.
 3. The compound according to claim 2, wherein the compound isrepresented by formula (II):

wherein p represents an integer from 1 to
 10. 4. The compound accordingto claim 3, wherein the compound is selected from the group consistingof: 1-[2-(2-[¹⁸F]fluoropyridin-3-yloxy)ethyl]-pyrrole-2,5-dione;1-[4-(2-[¹⁸F]fluoropyridin-3-yloxy)butyl]-pyrrole-2,5-dione;1-[5-(2-[¹⁸F]fluoropyridin-3-yloxy)pentyl]-pyrrole-2,5-dione;1-[6-(2-[¹⁸F]fluoropyridin-3-yloxy)hexyl]-pyrrole-2,5-dione;1-[(2-[¹⁸F]fluoropyridin-3-yloxy)methyl]-pyrrole-2,5-dione; and1-[3-(2-[¹⁸F]fluoropyridin-3-yloxy)propyl]-pyrrole-2,5-dione.
 5. Thecompound according to claim 2, wherein the compound is represented byformula (III):

wherein q and r each independently represent an integer from 0 to
 10. 6.The compound according to claim 5, wherein the compound is selected fromthe group consisting of:1-{4-[2-(2-[¹⁸F]fluoropyridin-3-yloxy)-ethyl]phenyl}pyrrole-2,5-dione;1-[4-(2-[¹⁸F]fluoropyridin-3-yloxymethyl)-phenyl]pyrrole-2,5-dione; and1-[4-(2-[¹⁸F]fluoropyridin-3-yloxymethyl)-benzyl]pyrrole-2,5-dione. 7.The compound according to claim 2, wherein the compound is representedby formula (IV):

wherein s represents an integer from 1 to
 10. 8. The compound accordingto claim 7, wherein the compound is1-[3-(6-[¹⁸F]fluoropyridin-3-yl)propyl]-pyrrole-2,5-dione.
 9. Thecompound according to claim 2, wherein the compound is represented byformula (V):

wherein t represents an integer from 0 to 10; and T is a —CH═CH— groupor a —C≡C— group.
 10. The compound according to claim 9, wherein thecompound is selected from the group consisting of:1-[3-(6-[¹⁸F]fluoropyridin-3-yl)allyl]-pyrrole-2,5-dione; and1-[3-(6-[¹⁸F]fluoropyridin-3-yl)prop-2-ynyl]pyrrole-2,5-dione.
 11. A kitcomprising a macromolecule and the compound according to claim
 1. 12.The kit according to claim 11, wherein the kit is a detection andanalysis kit for medical imaging.
 13. The kit according to claim 11,wherein the kit is a diagnosis kit.
 14. The kit according to claim 11,wherein the macromolecule is a biological macromolecule.
 15. The kitaccording to claim 11, wherein the macromolecule is a biologicalmacromolecule selected from the group consisting of an oligonucleotide,a protein, an antibody and a peptide.
 16. The kit according to claim 11,wherein the macromolecule is a macromolecule for recognition of aspecific site that exhibits target molecules associated with aparticular disease.
 17. The kit according to claim 11, wherein themacromolecule is a macromolecule for recognition of a specific site thatis selected from the group consisting of apoptosis sites, necrosis sitesor tumor sites.
 18. A process for preparing the compound according toclaim 1, wherein the process comprises: contacting a precursor compoundaccording to formula (Ia):

 wherein PR₁ and PR₂ each independently represent: a hydrogen or aprotective group, with the proviso that PR₁ and PR₂ are not both ahydrogen; or PR₁ and PR₂, together with the nitrogen atom, form a cyclicprotective group; Gp represents a leaving group capable of beingreplaced by a fluorine-18 atom; m represents an integer from 0 to 10; nrepresents an integer from 1 to 10; Y represents a monocyclic orbicyclic heterocyclic group selected from the group consisting ofimidazolyl, pyrazolyl, benzimidazolyl, pyridinyl, pyridazinyl,pyrimidinyl, pyrazinyl, triazinyl, quinolinyl, isoquinolinyl,cinnolinyl, quinazolinyl, quinoxalinyl and purinyl, wherein Y mayoptionally be substituted with one or more substituents selected fromthe group consisting of hydrogen, halogen, phenyl, C₁-C₆ alkyl, C₁-C₆alkoxy, aryloxy, amino, mono- or di(C₁-C₆ alkyl)amino, mono- ordi(aryl)amino, thio, C₁-C₆ alkylthio, arylthio, formyl, C₁-C₆alkyl-carbonyl, arylcarbonyl, carbonyl, C₁-C₆ alkoxy-carbonyl,aryloxycarbonyl, C₁-C₆ alkylamino-carbonyl, arylaminocarbonyl andtrifluoromethyl; and X represents a radical of the following formula:(U)_(a)—((CR₁R₂)_(b)—(V)_(c))_(d)—((CR₃R₄)_(e)—(W)_(f))_(g)—  wherein a,b, c, d, e, f and g each independently represent an integer from 0 to10; and U, V and W each independently represent —NR₁—, —O—, —S—,—N(—O)—, ethynyl, —CR₁═CR₂—, —(C═O)—, —(C═S)—, —C(═NR₁)—, —C(═O)O—,—(C═S)S—, —C(═NR₁)NR₂—, —CR₁R₂—, —CR₁OR₂— or —CR₁NR₂R₃—, wherein R₁, R₂,R₃ and R₄ are each independently selected from the group consisting ofhydrogen, halogen, phenyl, C₁-C₆ alkyl, C₁-C₆ alkoxy, aryloxy, amino,mono- or di(C₁-C₆ alkyl)amino, mono- or di(aryl)amino, thio, C₁-C₆alkylthio, arylthio, formyl, C₁-C₆ alkyl-carbonyl, arylcarbonyl,carbonyl, C₁-C₆ alkoxy-carbonyl, aryloxycarbonyl, C₁-C₆alkylamino-carbonyl, arylaminocarbonyl and trifluoromethyl. with asource of [¹⁸F]-labeled fluoride anions (F) to provide a compoundaccording to formula (Ib):

removing the protective group(s) PR₁ and/or PR₂ from the compoundaccording to formula (Ib) to provide a compound according to formula(Ic):H₂N—(X)_(m)—(Y)_(n)—¹⁸F  (Ic); and reacting the compound according toformula (Ic) with a reactant capable of providing a maleimido group froman amino group, to yield the compound according to claim
 1. 19. Theprocess according to claim 18, wherein the protective group(s) PR₁and/or PR₂ is/are selected from the group consisting oftert-butoxycarbonyl (BOC) and fluorenylmethoxycarbonyl (FMOC).
 20. Theprocess according to claim 18, wherein the protective groups PR₁ andPR₂, together with the nitrogen atom, form a phthalamido protectivegroup.
 21. The process according to claim 18, wherein Gp is selectedfrom the group consisting of a halogen, a mesyl group, a tosyl group, atriflate group, a nitro group and an ammonium salt.
 22. The processaccording to claim 21, wherein Gp is an ammonium salt and the ammoniumsalt is trimethylammonium trifluoromethanesulphonate.
 23. The processaccording to claim 18, wherein the source of [18F]-labeled fluorideanions (F) comprises the fluoride anions (F) and a counterion.
 24. Theprocess according to claim 23, wherein the counterion is a cationselected from the group consisting of rubidium, tetrabutylammonium,potassium, sodium and lithium.
 25. The process according to claim 23,wherein the counterion is a cation selected from the group consisting ofpotassium, sodium and lithium, and the cation is stabilized by acryptand or a crown ether.
 26. The process according to claim 18,wherein said removing is carried out by deprotecting the compoundaccording to formula (Ib) with trifluoroacetic acid (TFA) in a solventfor a period of 1-5 minutes to provide the compound according to formula(Ic).
 27. The process according to claim 26, wherein the solvent isdichloromethane.
 28. The process according to claim 18, wherein thereactant capable of providing a maleimido group from an amino group isselected from the group consisting of N-methoxycarbonylmaleimide andsuccinimide.
 29. The process according to claim 18, wherein saidreacting is carried out in a solvent with heating at a temperature of100-200° C. for a period of 1-20 minutes.
 30. The process according toclaim 29, wherein the solvent is xylene or tetrahydrofuran.
 31. Theprocess according to claim 18, wherein said reacting is carried out in atwo-phase mixture at ambient temperature for a period of 3-15 minutes.32. The process according to claim 31, wherein the two-phase mixturecomprises dioxane and aqueous sodium bicarbonate.
 33. The processaccording to claim 18, wherein the precursor compound according toformula (Ia) corresponds to a compound according to formula (IIa):

wherein p represents an integer from 1 to
 10. 34. The process accordingto claim 18, wherein the precursor compound according to formula (Ia)corresponds to a compound according to formula (IIb):

wherein p represents an integer from 1 to
 10. 35. The process accordingto claim 18, wherein the precursor compound according to formula (Ia)corresponds to a compound according to formula (IIIa):

wherein q and r each independently represent an integer from 0 to 10.36. The process according to claim 18, wherein the precursor compoundaccording to formula (Ia) corresponds to a compound according to formula(IIIb):

wherein q and r each independently represent an integer from 0 to 10.37. The process according to claim 18, wherein the precursor compoundaccording to formula (Ia) corresponds to a compound according to formula(IVa):

wherein s represents an integer from 1 to
 10. 38. The process accordingto claim 18, wherein the precursor compound according to formula (Ia)corresponds to a compound according to formula (IVb):

wherein s represents an integer from 1 to
 10. 39. The process accordingto claim 18, wherein the precursor compound according to formula (Ia)corresponds to a compound according to formula (Va):

wherein t represents an integer from 0 to 10; and T is a —CH═CH— groupor a —C≡C— group.
 40. The process according to claim 18, wherein theprecursor compound according to formula (Ia) corresponds to a compoundaccording to formula (Vb):

wherein t represents an integer from 0 to 10; and T is a —CH═CH— groupor a —C≡C— group.
 41. A method of labeling a macromolecule comprisingcoupling the compound according to claim 1 to the macromolecule.
 42. Themethod according to claim 41, wherein the macromolecule is a biologicalmacromolecule.
 43. The method according to claim 41, wherein themacromolecule is a biological macromolecule selected from the groupconsisting of an oligonucleotide, a protein, an antibody and a peptide.44. The method according to claim 41, wherein the macromolecule is amacromolecule for recognition of a specific site that exhibits targetmolecules associated with a particular disease.
 45. The method accordingto claim 41, wherein the macromolecule is a macromolecule forrecognition of a specific site that is selected from the groupconsisting of apoptosis sites, necrosis sites or tumor sites.